This invention relates to a method of manufacturing power semiconductor devices composed of such power semiconductor elements as IGBTs or GTOs.
Since the power semiconductor device is required to have a great current-carrying capability, in general, its area is larger than that of any other semiconductor device. In the exposure step in forming power semiconductor devices in a wafer, an exposure apparatus that exposes the entire surface of the wafer at a time at the projection reduction ratio of 1:1 (hereinafter, referred to as the 1:1 entire surface exposure apparatus) is used.
In the 1:1 entire surface exposure apparatus, the minimum dimension that can be exposed is approximately 10 .mu.m, and the alignment allowance is approximately 1 .mu.m. The accuracy of that order is sufficient for manufacturing conventional power semiconductor devices.
Recently, there have been strong demands toward improving the functions of power semiconductor devices, and therefore it is necessary to make power semiconductor elements much finer. As a result, the exposure accuracy tends to be more strict. Specifically, exposure accuracy with a minimum exposure dimension of nearly 1.0 .mu.m and alignment allowance of nearly 0.5 .mu.m has been required.
To meet such requirements, it is more desirable to use the reduction projection-type exposure apparatus (hereinafter, referred to as the stepper exposure apparatus) with the projection reduction ratio 5:1 that the 1:1 entire surface exposure apparatus.
The maximum size that can be exposed in one shot of the stepper exposure apparatus is approximately 15 mm.times.15 mm. Therefore, when a power semiconductor device is larger than the maximum size, it is impossible to expose all of the element areas on the wafer in one shot. Thus, to expose all of the device areas, more than one shot must be taken.
Furthermore, the power semiconductor device has a non-repetitive pattern such as a junction termination area at the peripheral portion thereof. Therefore, in general, even if more than one shot is taken, the same patterns are not repeated. Accordingly, in the worst case, one exposure step also requires as many exposure masks as more than one shot.
As a result, the stepper exposure apparatus alone has a disadvantage in that the work efficiency drops significantly although the exposure accuracy is higher.
Furthermore, as power semiconductor elements will be made much finer in the future, it is expected that conventional manual repairing will be more difficult and consequently repairing efficiency will deteriorate.